*{
    margin: 0;
    padding: 0;
}
.wapper{
    position: relative;
    width: 400px;
    height: 400px;
    margin: 100px auto;
}
.pan{
    width: 100%;
    height: 100%;
}
.pan img{
    width: 100%;
    height: 100%;
}
.btn{
    position: absolute;
    width: 130px;
    height:130px;
    left: 50%;
    top: 50%;
    margin-left: -65px;
    margin-top: -65px;
    cursor: pointer;
}
.btn img{
    position: absolute;
    width: 100%;
    top:-23px;
}